Determination of Neuroepithelial Cell Fate: Induction of the Oligodendrocyte Lineage by Ventral Midline Cells and Sonic Hedgehog

Abstract

Near the floor plate of the embryonic neural tube there is a group of neuroepithelial precursor cells that are specialized for production of the oligodendrocyte lineage. We performed experiments to test whether specification of these neuroepithelial oligodendrocyte precursors, like other ventral neural cell types, depends on signals from the notochord and/or floor plate. We analyzed heterozygous Danforth's short tail (Sd/+) mutant mice, which lack a notochord and floor plate in caudal regions of the neural tube, and found that oligodendrocyte precursors did not appear at the ventricular surface where there was no floor plate. Moreover, oligodendrocytes did not develop in explant cultures of Sd/+ spinal cord in the absence of a floor plate. When a second notochord was grafted into an ectopic position dorsolateral to the endogenous notochord of a chicken embryo, an additional floor plate was induced along with an ectopic focus of oligodendrocyte precursors at the ventricular surface. Oligodendrocytes developed in explants of intermediate neural tube only when they were cocultured with fragments of notochord or in the presence of purified Sonic hedgehog (Shh) protein. Thus, signals from the notochord/floor plate, possibly involving Shh, are necessary and sufficient to induce the development of ventrally derived oligodendroglia. These signals appear to act by specifying the future fate(s) of neuroepithelial cells at the ventricular surface rather than by influencing the proliferation or differentiation of prespecified progenitor cells in the parenchyma of the cord.

Spatiotemporal gradient of oligodendrocyte differentiation in chick optic tectum requires brain integrity and cell‐cell interactions

“…It is necessary now to determine the nature of the interactions that cannot be broken before E10 and the nature of the inhibitory influences that are lifted to allow tectal oligodendrocyte differentiation. It also needs to be determined whether or not local sonic hedgehog (Shh) signaling is responsible for the appearance of tectal oligodendrocytes, as it has been suggested for the telencephalon (Tekki-Kessaris et al, 2001), metencephalon (Davies and Miller, 2001), and spinal cord (Pringle et al, 1996;Soula et al, 2001). …”

Sonic hedgehogRegulates Proliferation and Inhibits Differentiation of CNS Precursor Cells

“…5E). Several lines of evidence indicate that Shh is necessary and sufficient for ventral neuron (in particular motor neuron) and oligodendrocyte induction (Marti et al, 1995b;Roelink et al, 1995;Chiang et al, 1996;Ericson et al, 1996;Poncet et al, 1996;Pringle et al, 1996;Orentas et al, 1999). Thus, we determined whether ventral motor neurons or oligodendrocytes were induced in Shh-Tg mice.…”

“…Shh is essential for maintenance of notochord and prechordal mesoderm (Chiang et al, 1996) as well as the induction of floorplate and ventral neuronal populations that form at different positions along the anterior-posterior (AP) axis of the neural tube (Echelard et al, 1993;Roelink et al, 1994Roelink et al, , 1995Marti et al, 1995b;Chiang et al, 1996;Ericson et al, 1997;Jessell and Lumsden, 1997). In addition, there is evidence that Shh signaling may specif y oligodendrocyte precursors (Poncet et al, 1996;Pringle et al, 1996). Shh signal transduction is complex (Tabin and McMahon, 1997).…”

Expression analysis of Sulf1 in the chick forebrain at early and late stages of development

“…However, we do not observe any overlap between the plp/dm20 domain of expression and Sulf1-positive bands in prosomere 1. In the chick developing brain, the ventricular domains of plp/ dm20 expression correspond to restricted foci that give rise to oligodendrocytes, closely associated to the domain of Shh expression (Poncet et al, 1996;Pringle et al, 1996;Perez-Villegas et al, 1999). In mouse, PDGFR␣ and plp/dm20 have been shown to be expressed in distinct oligodendroglial precursors (Spassky et al, 1988); therefore, we cannot exclude that plp/dm20 and Sulf1 identify distinct neural precursors with oligodendroglial potential.…”